In the golf ball manufacturing process, it is common practice to form the cover of the ball using injection molding. A mold comprising a pair of parallel plates containing opposed hemispherical cavities is used to form a spherical cavity within which a golf ball core is suspended by retractable pins. Fluid thermoplastic material is supplied to the cavity to form the cover layer of the ball. After the thermoplastic material sets, the plates are separated and the golf ball is removed from the cavity.
The present invention relates to an improved mold for simultaneously injection molding a plurality of golf balls which have improved surface characteristics and minimal imperfections.
Injection molds for forming golf balls are well-known in the patented prior art. The Lavallee et al U.S. Pat. No. 5,827,548, for example, discloses a retractable pin golf ball injection mold wherein thermoplastic material is delivered to a plurality of spherical cavities defined by upper and lower support plates via a balanced runner system to form the cover layers on golf ball cores arranged in the cavities. Each cavity has a number of gates defined at the parting line defined where the plates meet at the equator of the golf ball. The balanced runners allow the thermoplastic material to be evenly supplied to cavities so that a number of golf balls are formed simultaneously. Coolant is circulated through the plates to reduce the cure time for the cover layer. An ejector mechanism is also provided to eject the finished golf balls from the cavities and excess thermoplastic material from the runner system.
The Giza U.S. Pat. Nos. 4,959,000 and 5,147,657 disclose retractable pin molds for golf balls where the gate valves are at the poles of the golf ball.
While the prior devices operate satisfactorily, they still possess inherent drawbacks which lead to imperfections in the golf ball surface and which limit the production capacity owing to the time required to finish the golf balls. More particularly, the plurality of parting line gates in the prior Lavallee et al device result in gate vestiges in the ball surface. These must be trimmed or otherwise removed to finish the golf ball. Moreover, the excess thermoplastic material from the runners must be removed therefrom and then re-heated to a fluid state for use in subsequent injection molding operations.
The present invention was developed in order to overcome these and other drawbacks of the prior golf ball molds by providing a golf ball mold in which a single direct cavity gate is provided at the pole of the ball in the upper support plate.
Accordingly, it is a primary object of the present invention to provide an injection mold for simultaneously molding the cover onto a plurality of golf balls. The mold includes upper and lower support plates each of which contain a plurality of hemispherical cavities which are adapted to mate to define a plurality of spherical cavities when the plates are brought together. Retractable core pins are arranged in each of the cavities to support a core of a golf ball. A direct cavity gate is arranged at the top dead center of the upper hemispherical cavity to supply fluid thermoplastic material to the cavity to form the cover layer on the golf ball core. A valve pin is arranged in the gate and is operable between a first position wherein the pin extends into the cavity to engage the core and to allow thermoplastic material to enter the cavity and surround the core, a second position wherein the pin is retracted into the upper support plate out of contact with the core to allow thermoplastic material to fill the cavity, and a third position between the first and second positions wherein the pin closes the gate to stop the supply of thermoplastic material into the cavity.
According to a further object of the invention, the valve pin has a contoured lower end which forms a pole dimple on the golf ball surface when the valve pin is in the third position. In addition, a control mechanism is provided to displace the valve pin between the first, second, and third positions and to displace the retractable core pins.
It is yet another object of the invention to provide two types of core pins. In a first embodiment, the core pins are arranged laterally and equally spaced about the lower hemispherical cavity. In a second embodiment, the core pins are equally spaced about the lower hemispherical cavity and have longitudinal axes arranged substantially perpendicular to the parting lines. A vent pin is also provided in the lower plate and communicates with the cavity to vent air therefrom as thermoplastic material is supplied to the cavity.